I have not been able to find the answer to this question, so maybe there isn't a simple one but...

Is there a general correlation between the A/R size of a T3 exhaust housing and the A/R of a T4 footprint? For instance, generally speaking I've been told that an undivided housing will have the same spool characteristics as a fully divided housing, one size larger.

Recently I was told that a .86 undivided flows the same as a 1.32 divided, which is more than one "size".

Since the footprint of a T4 is only slightly larger (see picture), would a comparable T3 A/R be slighly larger as well?

 

forgot the pic

 

I think you've been told wrong. It's said that a "divided" manifold will spool as quick as a "NONdivided" of 1 size smaller. There would be no incentive to go with a more expensive divided manifold, if that were the case. I think they flow pretty similar between same A/R sizes, within same turbo family, all things being equal.

 

Yeah, I think we said the same thing... just a different order, but I agree with you.

I was mostly concerned with the A/R thing. Being that it's a ratio and all, but if the entrance area is nearly the same, the I would expect the A/R's between the two families (T3 and T4) to flow the same all else equal... I would expect the A/R's to be the same in a given family, I"m more concerned with across the families...

 

You cannot simply compare A/R's from one family of turbos to another. You also have to consider turbine wheel trim. To me that's more important than A/R's when it comes to flow. A/R's in my opinion affect response and power band more than flow.
At certain HP levels I've seen different A/R housings have little affect on power output but turbine wheel trim would have a great influence on power output.

crispeed
87 Rx-7 TII
9.204@150.47mph
2600lbs
un-tubbed

 

Thankyou for clarifying crispeed.

FWIW, I was trying to switch a 1.0 AR T3 undivided to a T4 divided (with the same turbine wheel trim) and potentially increase spool times without choking the engine on the top end and maybe even gain something. Yes I have checked and can do this... I just didn't know where to start A/R wise on the T4. My options in the T4 are 1.0,l 1.15 and 1.32 divided. Since this is a street car, I'll probalby start with the 1.0 and go from there.

Sounds like there isn't an exact science so I'll have to experiment a bit. Thanks for the insite.

 

Which stage T-3 turbine wheel do you have?

crispeed

 

Heh, I was a little bit heistant to say since it will be asking for another flame but....

I'm actually asking in regard to the Gt35/40

Most people get it with the 1.06 and yes it works great. RPM in AUS seems to recomend the .82 for a street car saying that the spool is even that much faster than the 1.06 that everyone raves about.

" a .82 will smoke the tyres at half throttle."

There was just a huge post about how much better a tuned manifold/divided housing was than an undivided, untuned setup. Everyone agrees this is true.

So despite spool being awesome on the run of the mill 35/40 with a 1.06, it can be made better... with the .82 as shown in Aus. Sure seems to me that a 1.0 T4 divided or *maybe* even the 1.15 T4 divided setup will spool like the .82 and have the top end potential of the 1.06.

I was told, by RPM, that the turbine manifold from a TA45, or a T51 could be used and that's where all this has come from. I don't know if it had to be modified or not. The additional cost to the turbo was not that much and if it should improve performance, then I'm all for it.

-chris

 

I kind of figured that out!

The GT turbine wheels are not your average run of the mill T-3 turbine wheels. Those new wheels flow and spool a lot better than most of the older designed wheels. You just got to be honest about HP goals and boost response and pic the turbine wheel that's needed.

crispeed
87 RX-7 TII
9.204@150.47mph
2600lbs
un-tubbed

 

why not just get a straight gt40 then?

 

Because the Gt40 isn't available. I tried that route already

Guess I wasn't being sneaky enough!

I do realize that the new garrett wheels are different. I guess I also thought that RPM would only be changing the housing... ie i assumed that the TA45 used the same turbine wheel as the 35/40, and the only difference was that I was getting a divided housing with a T4 footprint. I should clarify exactly what is changed: ie if the turbine wheel will be the same.

Part of my problem is certianly that I am an engineer, and I am convinced that if a complete system is designed using the best of the best,then that system will be "the" best.

It only seems to me that adding a tunned, divided manifold, and a divided turbine housing to an already great setup will make it that much better. That's all.

I've already designed a manifold utilizing the knowledge I've gained from this forum: runner length, diameter, everything being equal etc. and have a shop lined up for fabrication. I just want the best possible turbo to top it off and jumping on the bandwagon of "the Gt35/40 is the best street/strip turbo" just doesn't fly with me when there are aspects that don't fit the agreed upon "ideal" for turbo spool and top end.

To my knowledge no one has tried to run a 35/40 (and the associated BB CHRA) with a divided housing. Sure it's good, but *what if* it could be better with just a little more thought.

That's what I'm trying to determine....


*edit* crispeed, check your PM's

 

you can get a gt40 from any authorized garrett u.s. distributor. it won't spool as fast as the 35/40 though, even w/ dividided manifold. the whole point of the 35/40, and t3/t4's in general is that they spool faster than straight t4's.

 

I disagree.

Have you tried to get a Gt40? Everyone you talk to will tell you it can't be had... several people on this forum have tried to get one, no one has been successful. They will tell you the parts do not exist to make a BB CHRA. Furthermore, they apparently don't have the BB CHRA. If you read the catalog, the only ones that have a BB CHRA are the GT35 (and variants of course) and GT42.

The whole point of the 35/40, IMO, is not that it's T3... it's the BB center linked to a good compressor with a newly designed turbine wheel for higher efficiency. You can make a 60-1 spool just as fast as a 35/40 if you want to put a small enough T4 housing on it.

Read about the Gt42 or talk to Marco. He has that thing spooling nearly as fast as a 35/40 with a HUGE compressor and a manifold larger than a T4.... how does he do it? Because the manifold is tuned and fully divided into a fully divided housing... not b/c he put a small t3 undivided housing on it.

 

YUP